A chemical equilibrium in Chemistry is always described as dynamic because it changes when the external constraints like change in temperature, pressure or concentration is imposed on the system changes.
Now a system attains chemical equilibrium when the rate of forward reaction equals the rate of backward reaction in such a way that the concentration reactant and products remain constant.
System in dynamic chemical equilibrium neutralizes changes by either shifting to right or left when conditions like changes in Temperature, Pressure and concentration is imposed on the system.
We need to understand that we have two types of equilibrium;
Static equilibrium is the type of equilibrium in which the equilibrium is permanent and steady.
Dynamic equilibrium is the type of equilibrium in which the equilibrium is temporal and is subject to change.
Why is a reversible chemical reaction said to be in dynamic equilibrium?
A reversible chemical reaction is said to be in dynamic chemical equilibrium because changes imposed can upset the equilibrium position for a while before the system regains the equilibrium.
We need to recall that chemical equilibrium in systems are attained but also the equilibrium position can temporarily be altered by imposing changes in external constraints like temperature, pressure and concentration however the system tends to regain the equilibrium position.
The reason why reversible chemical reactions are said to be in dynamic equilibrium is because he equilibrium is not permanent but do change as changes in external constraint are imposed.
This reason is supported by a principle called Le Chatelier’s Principle which states that when an external constraint such as change in Temperature, pressure or concentration is imposed on a system in equilibrium, the system will shift so as to annul the effect.
However, the characteristics or properties of a system in dynamic equilibrium do not really change though equilibrium position can be altered.
Specific examples why some reversible chemicals are said to be in dynamic equilibrium.
There are three changes that cause a system to be in dynamic equilibrium, these changes are changes in temperature, pressure and concentration and I am going to give three basic examples of how these cause a system to be or remain in dynamic equilibrium.
|How these constraints affect systems in chemical equilibrium
|Effect of Temperature
|Effect of Temperature Recall
Endothermic reaction +ve is favoured by increase in temperature
Exothermic reactions -ve is favoured by decrease in temperature X + Y===Z enthalpy change H =+ve What is the effect of increasing temperature on dynamic equilibrium of chemical systems? Consider this reaction X + Y===Z enthalpy H =+ve Increasing temperature. Increase in temperature will favour forward reaction (shifting the equilibrium to the right) producing more of Z because forward is endothermic. Reason Because forward reactions is endothermic Decreasing Temperature Decrease in temperature will favour backward reaction (shifting the equilibrium position to the left producing more of A and B) Reason Because backward is exothermic.
|Effect of Concentration
|Effect of concentration Concentration is another factor that affects the dynamic chemical equilibrium of systems. What is the effect of concentration on the dynamic equilibrium of chemical reactions?
Increase in concentration on one side favours the other side
Decrease in concentration on one side favours same side Example Consider the reaction MgCO3 ===MgO +CO2 Effect of What is the effect of increasing the concentration (mass) of MgCO3 on equilibrium position? It will shift the equilibrium to the right producing more of CaO and CO2 I.e favoring forward reaction What is the effect of decreasing the amount of MgO formed? it will still favour the forward reaction shifting the equilibrium position to the right
|Effect of pressure
|Effect of Pressure Recall
When you increase in pressure, it favours the side with less no of moles or volume
When you decrease pressure, it favours side with higher no of moles Effect of Pressure on chemical equilibrium 2SO2 + O2 è 2SO3 increase in pressure Increase in pressure will shift the equilibrium position to the right or favours forward reaction producing more of SO3 because it is the side with less no of moles Decrease in pressure
Decrease in pressure favors backward reaction producing more of SO2 and O2 because it is the side with higher no of moles
So, these are the reasons why a chemical system is said to be in dynamic chemical equilibrium. Why a Chemical equilibrium is described as dynamic also connotes the unstable nature due to the annulling of the effect caused by imposing these changes.